Human-machine interfaces that enable a user to interact with a device are well-known in the art for a plurality of different types of devices. For each of said devices, specially adapted human-machine interfaces have been developed that account for the ergonomic characteristics of the human user and thus allow for an efficient and comfortable interaction of the user with the device.
In particular in most of the electronic devices that process textual information, as for instance desk-top or lap-top computers, or hand-held multimedia devices such as Personal Digital Assistants (PDAs) or mobile phones, some type of alphanumeric keyboard, comprising a plurality of keys that are labelled with one or more letters, numbers or symbols, are used to allow the user to enter instructions to be executed by said electronic device or to generate textual information, as for instance documents, databases, messages or the like.
When keys of said alphanumeric keyboard are pressed with the fingertips of the user's hands, information associated with said pressed keys, and usually represented on said keys in the form of a key label, is generated in the shape of electric signals that are transferred to the electronic device via a wired or wireless, for instance optical, interface.
In most text processing applications, after a key is pressed by a user, the information associated with said pressed key is instantly displayed on a display of said electronic device, for instance in a window of a computer screen or a hand-held device. As a matter of fact, even when said keyboard is a touch-screen, said keyboard and said display or display area that show the entered information are spatially separated. For instance, in case of a touch screen keyboard, where the keyboard is integrated into a display, a first area of said display, for instance the lower part of the display, will be dedicated to said keyboard, wherein a second area, for instance the upper part of said display, will be consumed by said window that depicts the entered information.
In state-of-the-art desk-top or lap-top computer applications, the keyboard is generally positioned substantially plane on a table, and the area of the display is positioned substantially perpendicular to the area of the table.
Thus when entering text, which is to be displayed on a display of an electronic device, via a keyboard, a frequent change of the look direction or even the entire head orientation is required to control (with look direction to the keyboard) if the fingertips are positioned on the correct keys of the keyboard, so that the desired keys are pressed, and to control (with look direction to the display) if the text entered via the keyboard is actually correct. The frequency of said change in the look direction generally decreases with increasing skills of the typist, in the extreme case of a very skilled typist requiring basically no checking back on the fingertip positions on the keyboard at all; but generally most of the mediocre typists have to check back the fingertip positions on the keyboard when more rare keys such as symbol keys or certain control keys have to be pressed.
Frequently changing the look direction does not only increase the typing time and sensitivity to typing errors, but also often requires additional re-focusing of the eye due to different distances of the eye from the keyboard and display, respectively. Consequently, a high frequency of change in the look direction also causes eyestrain.
These problems are even more pronounced in the context of hand-held multimedia devices. A first group of such hand-held devices is equipped with keypads (small keyboards) that consist of extremely small keys, the position of which is generally not standardized. The aggravation of the above-stated problems with such keypads is obvious. A second group of such hand-held devices comes with foldable keyboards, with problems comparable to the context of desktop and laptop computers, or uses alternative solutions such as for instance optically projected virtual keyboards. Such virtual keyboards basically comprise the following components: a first component projects an image of the keys of a keyboard onto a plane area, e.g. a table surface, a second component generates a beam of infra-red light that is reflected by the fingers of the user resting on the projected keyboard, and a third component receives the reflections of said beam of infrared light from the fingers of said user to determine which virtual keys are pressed by the user. In addition to the problems emphasized above in the context of desktop and laptop computer keyboards, in this type of keyboard the fingers themselves may disturb the projection of the keyboard image onto the plane surface, so that even when looking towards the keyboard, it may be difficult for the user to decide on which keys his finger tips are actually resting.